The invention relates generally to peristaltic pumping systems, and more particularly, to a pumping segment incorporated into a peristaltic pumping system that facilitates efficient and accurate peristaltic pumping of fluids as well as provides for regulation of fluid flow and an effective interface for sensing fluid pressure.
In traditional medical and industrial applications, peristaltic pumps accomplish pumping of fluids by sequentially occluding a generally round tube containing a fluid, which results in advancing fluid through the tube. It is generally the case that the tube becomes completely occluded, wherein opposing walls of the tube are brought into contact, thereby sealing the tube shut and preventing back flow. Since round tubing requires a significant degree of deformation in order to accomplish the sealing of the tube, high stress levels can be reached in the walls of the tubing.
Due to these high stress levels, the physical dimensions of the tubing may change over time, and as a result, fluid flow and fluid pressure may be affected causing deviations from expected conditions. To address this problem, some systems incorporate a tubing segment comprising materials possessing high strength and resiliency. Such tubing, however, is generally expensive relative to conventional tubing. Moreover, by merely employing a round tubing segment having greater strength and resiliency, the problems associated with the force and stress required to compress a round tube are not fully addressed.
In other applications, the pumping systems employ a separate fluid chamber contained in a pumping segment that connects to conventional tubing and that operates as structure for facilitating pumping. The typical configuration of these pumping systems is that of a piston cooperating with the chamber to pump fluid. These chambers address the problems associated with the force and stress levels in conventional round tubing but are, however, also relatively expensive to produce. In addition, systems incorporating such chambers are limited since their designs are somewhat more complex and they are more difficult and expensive to manufacture.
In a peristaltic pumping system, it is desirable to control or monitor fluid line pressure. Conventional peristaltic pumping systems typically use separate devices for accomplishing this in which one device facilitates peristaltic pumping and another device that facilitates the measurement of line pressure. Such conventional systems typically take pressure measurements directly from the tubing. However, where a peristaltic pumping system takes pressure measurements directly from the tubing, tubing dimensions and elastic properties must be accurately and closely controlled to assure precise measurements.
Also, in order to take accurate pressure measurements, it is important that the peristaltic pumping system employs structure that assures an effective interface between the fluid pressure and the pressure sensing element. Conventional systems that take fluid pressure measurements directly from the tubing are limited, since they often lack an optimum interface between the tubing and sensor. Generally speaking, a significant negative pressure that may accumulate in the tubing can cause the interfacing structure of conventional systems to separate from the sensor, thereby preventing transfer of fluid pressure to the sensor.
In peristaltic pumping systems, it also may be desirable to provide an automatically operated flow control device that operates on the fluid conduit but which also permits manual operations. Conventional systems generally incorporate fluid flow regulation capabilities into a separate device from those functioning to facilitate the peristaltic pumping of fluids and those functioning to facilitate measurement of fluid line pressure. Such conventional fluid flow regulators heretofore provided have utilized various clamp, lever or roller arrangements for partially or completely crimping flexible round tubing at a point upstream from the pumping mechanism. One conventional flow control device includes a ribbed roller having ends which travel within laterally spaced apart furrows formed in vertical sidewalls of a housing through which flexible round tubing of the pumping system passes. The housing also includes an opposing wall that is inclined at an angle to the path of the roller and the housing receives the round tubing between the path of the roller and the opposing wall. By varying the position of the roller along the furrows, the degree of tubing closure and hence the flow rate of fluid through the system, can be controlled.
Flow control devices of this type, however, are limited in that the flexible tubing they act upon can be flattened or otherwise dimensionally deformed as a result of the compression force exerted by a clamp, lever or roller over a period of time. This deformation or creep may progress with time, with the result that the flow rate in the system changes from an expected rate, and the system therefore, requires the user to periodically readjust the flow control device in order to achieve desired flow rates.
Other fluid control devices embody a flexible round conduit that connects with and replaces a segment of conventional tubing and includes a cylindrical insert member disposed within the conduit. The cylindrical insert defines a channel for fluid flow, a portion of which has a progressively increasing cross-sectional area along its axis. An outer sleeve fits over the flexible cylindrical conduit and embodies a roller that slides within a track formed in the outer sleeve. By positioning the roller along the flexible cylindrical conduit, portions of the flexible conduit are forced into the channel defined by the cylindrical insert, thereby controlling fluid flow. This device, however, is limited since the cross-sectional area of the cylindrical conduit may change with time and therefore, require the user to make adjustments to achieve desired flow rates. Moreover, the device is limited since it embodies a relatively complex design having a number of interacting and moving parts that require high precision manufacturing with associated increased expense.
Accordingly, there remains a need for a single device that facilitates efficient and accurate peristaltic pumping of fluids over long periods of time, that provides an effective interface for sensing fluid pressure under varying conditions of line pressure, including negative pressure, and that provides regulation of fluid flow while minimizing system inaccuracies. The present invention fulfills these needs.